BANGOR, Maine — The family and friends of a Bradford man accused of slaying a Hudson man with whom he had an ongoing dispute more than 16 months ago packed a second-floor courtroom Monday at the Penobscot Judicial Center along with the family and friends of the victim.

Peter Robinson, 49, is accused of beating to death David Trask, 71, on Nov. 12, 2011, with a 15-pound, 58-inch-long crowbar in an alleged dispute over a right of way. His trial began Monday.

A jury of nine men and six women, including three alternates, was sworn in Monday and heard preliminary instructions from Superior Court Justice William Anderson.

Assistant Attorney General Andrew Benson told jurors that on at least three occasions in the 2½ years before Trask’s death, Robinson threatened to kill him and-or his brothers. The prosecutor said that the defendant wanted to create “his own personal, private fiefdom” on his property and keep others, especially hunters, out of the remote area.

“He waged a one-man war against trespassers,” Benson said of Robinson, who posted his land, installed game cameras and put a cable with a lock on it across the shared entrance road to his property and the parcels owned by others.

Trask had purchased a lot with a right of way adjacent to Robinson’s property in 2011, according to a previous BDN report.

“[On Nov. 12, 2011,] the defendant grabbed the wrecking bar, knocked David Trask to the ground, broke his ribs, and then, while David Trask was lying on the ground defenseless and unarmed, the defendant literally beat David Trask’s head in,” the prosecutor said in his opening statement.

Benson said that Robinson’s contention that he acted in self-defense was not valid.

“Under Maine law you have an obligation to retreat from a threat if you can do so safely unless you are in your home,” he said. “If you provoked the incident, you are not entitled to use deadly force.”

Defense attorney Thomas Hallett of Portland called the victim and his brothers “a band of bullies” determined to force Robinson off his land in his opening statement. He told jurors that Robinson and his wife, Cheryl Robinson, had decided to move when David Trask died because they feared for their safety.

The couple still owns the property, Hallett said after court adjourned Monday.

Hallett said that the day he was killed, the victim was using the large crowbar and a sledgehammer to make holes in the ground near a culvert to put up fencing so snowmobilers could tell where the edge of the road was in the winter. When Robinson went to speak with Trask about his not reconnecting the cable across the road, Trask threatened to kill Robinson, the defense attorney told the jury.

“Pete could reasonably fear that his life was in jeopardy,” Hallett said. “On his right hip David Trask, was wearing a black holster and he had a utility knife and a silver knife in his pocket. Pete thought he had a gun.”

The victim did not have a gun, the defense attorney said, but his client did not know that at the time he struck Trask.

According to evidence presented Monday afternoon, “the holster” turned out to be a cellphone case attached to Trask’s belt. The cellphone was in the holder when detectives examined the scene.

The trial is scheduled to resume Tuesday morning. Dr. Michael Ferenc of the Office of the Chief Medical Examiner is expected to testify about wounds inflicted by the large crowbar. Trask died of head injuries with extensive fractures, according to a previously published report.

Ferenc found that Trask suffered at least three impacts consistent with a broad, heavy object hitting his face and chest, according to the affidavit filed five days after Trask died. One of them caused multiple rib fractures and another, to the mid-portion of the face, crushed the front of his skull and injured the brain. The third was to the chin and broke Trask’s jaw. His false teeth were found broken on the ground near his body.

Robinson has been free on bail since just before Christmas 2011. His bail conditions required that he live in York County and have no contact with a long list of relatives of the victim and potential witnesses.

Last week, Anderson modified those conditions in his chambers so it would be more convenient for Robinson to attend the trial. Hallett said Thursday after the hearing on pretrial motions that he believed the new conditions would ensure his client’s safety during the trial.

The trial is scheduled to last six days but might take longer since the prosecution and the defense have listed a total of 125 potential witnesses.

Hallett declined Monday after court adjourned for the day to say whether Robinson would take the stand in his own defense.

If convicted of murder, Robinson could spend between 25 years and life in prison.